Usually, the can end 2 of an ordinary packed can is seamed to a can body through a pre-seaming step conducted by a first seaming roll as shown in FIG. 1 and a final seaming step conducted by a second seaming roll 5.
More specifically, the seaming is conducted in accordance with the following process. As shown in FIG. 1, the can body 1 is mounted on a lifter plate 6 and the can end 2 is mounted on the can body 1. Then, as shown in FIG. 2, the seaming chuck 3 is fitted in the recessed part of the can end 2 so as to clamp the can body 1 and the can end 2. Then, the seaming chuck is rotated around the axis of the can body and, as shown in FIG. 3 the first seaming roll 4 rotatably mounted a shaft 13 parallel to the can axis 15 is moved towards the can axis, thereby to bring the annular groove 11 of the first seaming roll into contact with the curling portion 9 of the rotating can end 2. Consequently, the rotation of the can end 2 is transmitted through friction to the first seaming roll 4 to rotate the latter in synchronism with the rotation of the can end 2. Consequently, the curling portion 9 and the shoulder portion 8 connected to the curling portion 9 is turned and rolled into the shape of the annular groove 11 of the first seaming roll 4 as shown in FIG. 3, thereby to complete the pre-seaming by the first seaming roll 4. Then, the first seaming roll 4 is separated from the can end and the second seaming roll 5, which is rotatably carried by a shaft 14 parallel to the can axis 15, is moved towards the can axis while the latter is held vertically. Then, as in the case of the first seaming roll 4, an annular groove 12 in the second seaming roll 5 is brought into pressure contact with the curling portion 9 of the rotating can end 2, thereby to frictionally drive the second seaming roll 5 in synchronism. Consequently, the curling portion 9 and the shoulder portion 8 connected to the curling portion 9 are turned and rolled in confirmity with the annular groove 12 in the second seaming roll 5 into the state as shown in FIG. 5 thereby to complete the seaming.
As has been described, the seaming chuck and the seaming roll are made to contact with the can lid so as to be frictionally driven by the latter in synchronism with the same. The friction between the can end and the seaming chuck and seaming roll takes place not only during the synchronous rotation but also before and after the synchronous rotation, i.e. when the apparatus is being started and stopped. Consequently, the friction surfaces of the seaming chuck and the seaming roll are worn down rapidly. The rate of wear is increased as the seaming speed is increased. The friction surface coarsened by wearing damages the coating film on the can end surface to make the same come off from the can end surface. This not only impairs the appearance due to rusting but also promotes the corrosion of the can body. In the worst case, the can body is perforated by corrosion to permit the contents to flow out of the can. Consequently, the can body is contaminated and the content is lost. In order to obviate this problem, it is necessary to renew the seaming tool, thereby incurring an increase in production cost. In addition, the renewal of the seaming tool necessitates a suspension of the operation of the production line which unfavorably impairs the achievement of the production plan.
As a measure for overcoming these problems of the prior art, it has been proposed to use a hard alloy having a large wear resistance as the material of the seaming tool. This measure, however, cannot overcome the problems satisfactorily.
Under these circumstances, various proposals have been made up to now, as in Japanese Utility Model Laid-Open No. 165539/1981, Japanese Utility Model Laid-Open No. 165540/1981, Japanese Utility Model Laid-Open No. 165541/1981 and Japanese Patent Laid-Open No. 44435/1982. Some of these proposals use TiC or TiN solely or in the form of a solid solution. Namely, in these proposals, the tool surface is coated with a layer of TiC or TiN by chemical evaporation method. This coating layer, however, is extremely thin and can withstand only a short use.